This invention relates to an integrated circuit chip for use as an electronic thermostat. Such a device indicates whether the ambient temperature is above or below a predetermined value (trip temperature).
There are many examples in industry where a need exists to know whether the ambient temperature is above or below a specific value. Many existing solutions involve the use of devices such as thermistors, thermocouples, RTDs and temperature-to-digital converters. These solutions involve the use of external components and end-user factory calibration. An example of a current solution is the National Semiconductor LM56 device, which requires the use of external resistors to set up the required trip temperature. Another example is the Maxim MAX6501, which is available with a number of fixed-temperature trip points typically at ten degrees Celsius intervals. In the case of temperature-to-digital converters, software development is also required. An example of this is the Dallas DS1620, which requires the end-user to program the required trip point.
The invention seeks to provide an integrated circuit for use as an electronic thermostat which needs no external set-up, calibration or programming by the end user. The invention also seeks to provide a thermostat which can be programmed with its trip temperature in the final package so that is it not susceptible, or less susceptible, to the drift which can occur when silicon chips are assembled into packages.
Accordingly, the present invention provides an integrated circuit chip comprising a temperature sensor for providing a signal whose magnitude is a function of the ambient temperature, a comparator having an output which changes state when the magnitude of the sensor signal exceeds a temperature-equivalent signal corresponding to a stored digital value, and a control unit for setting the stored digital value corresponding to a desired trip temperature.
The term xe2x80x9ctemperature-equivalent signalxe2x80x9d as used herein refers to a signal, which may be analog or digital, which is related to and derivable from a digital value. In particular, but not exclusively, it may be used to refer to an analog signal generated by converting a digital value using a digital-to-analog converter (DAC).